In semiconductor integrated circuitry, one time programmable (OTP) electronic fuse (e-fuse) is known as a critical device, which is often and generally used to build redundancy for various mission-critical components in a chip for self-repairing purpose in situations where a critical device fails; for improving overall yield of the integrated circuit (IC) chip by providing the chip with functionality of post manufacturing configuration; and for enabling programming of certain security features such as, for example, electronic chip identification (ECID). As complementary metal-oxide-semiconductor (CMOS) technology scales down and more recently the adoption of high-k metal gate, metal e-fuses are being gradually used to replace conventional salicided polysilicon e-fuses.
FIGS. 7(a) and 7(b) are simplified illustrations of a typical metal e-fuse, before and after being programmed, as is known in the art. Metal e-fuse 700 is normally composed of a metal link 703 (known in the art as “M2”) terminated at two ends 701 and 702 by vias (known in the art as “V1”) and wirings (known in the art as “M1”). Upon programming, as illustrated in FIG. 7(b), excessive current of electrons is driven through M2 metal link as a mean to induce electro-migration voiding at flux divergence sites. Frequently, such voiding develops at the bottom of a terminating via, such as void 710 at V1 via, where flux divergence usually occurs and where liner and metal coverage of V1 via may not be well controlled during manufacturing of V1 via and M2 metal link. Nevertheless, it has been observed as well that voiding sometimes may occur in the M1 or M2 wirings, impacting programming reproducibility of e-fuses that employ the structure shown in FIG. 7(a).
In general, there are mainly two types of metal e-fuses being reported so far that are both programmed by employing metal electro-migration (EM) mechanism under controlled flow of electron current. A first type of metal e-fuses functions through the creation of a void in the wire, such as copper (Cu) wire, by the wire EM (wire mode). A second type of metal e-fuse functions through the creation of a void in the via by the via EM (via mode). However, both types of e-fuse or e-fuse operation modes carry certain concerns and reliability issues including (1) programmability (voiding location being unpredictable) and (2) reliability (possibility of out-diffusion of metal after programming).
The major concern for the wire mode e-fuse includes that it is generally difficult to control and re-produce void location as well as void size in order to achieve tight distribution of post-programming e-fuse resistance. With a wide, and sometimes un-controlled, distribution of e-fuse post-programming resistance, it becomes very difficult to characterize reliability of such programmed e-fuse to provide any meaningful guarantee for the safe use of it. On the other hand, there is reliability issue as well with the via mode e-fuse. For example, it is hard to contain metal out-diffusion, usually copper, to prevent collateral damage to neighboring devices both during and post metal e-fuse programming. Such damages may include, for example, causing a neighboring metal line or via to change resistance, metal short or open, as well as ILD (intra or inter level dielectric) leakage increase or failure.